The invention relates to spray apparatus and more particularly to injected liquid chemical spray apparatus for use in agriculture or horticulture.
As an aid to precision farming it is known to provide chemical spray apparatus arranged to vary the rate at which a desired chemical is applied (for example according to local conditions or the ground speed of the spray apparatus) by injecting the chemical directly into the spray carrier or liquid e.g. water shortly before it is applied. In this the volume of spray carrier or liquid sprayed remains substantially constant in terms of volume per unit area and only the concentration of the sprayed chemical in the spray carried or liquid is varied.
It is known that chemical injection systems may operate with high or low pressure injection pumps. A high pressure injection pump can inject chemical close to the spray nozzle as it has sufficiently high pressure to overcome the pressure of the pumped water. Unfortunately, however, this makes calibration of the injection system difficult as any change in the back pressure of the system affects the output of the injection pump. Low pressure injection injects chemical before the sprayer""s main pump where the pressure remains virtually atmospheric. This allows accurate calibration of the amount of chemical mixed with the water but is slower acting than the high pressure injection since the chemical is injected a significant distance from the spray nozzle.
International patent application WO99/39834 provides spray apparatus of the kind in which chemical to be sprayed is injected into spray carrier or liquid before the mixture of liquid and chemical is sprayed, comprising a closed loop circulating system having a pump with an inlet and an outlet, a loop line connecting the pump inlet and outlet, a spray nozzle connected to the loop line downstream of the pump via a spray line, a spray liquid inlet connected to the loop line upstream of the pump and a chemical injection system connected to the loop line upstream of the pump, a venturi device having an inlet and an outlet in the loop line, and having a suction or side port, a return line connection to the spray line at a position adjacent to the spray nozzle and connection to the suction port of the venturi device, an agitation line connected between the loop line downstream of the venturi device and the spray line adjacent the spray nozzle and valve means in the spray line directing liquid flow to the spray nozzle to cause reverse flow through the agitation line past the spray nozzle and through the return line
An object of the present invention is to provide an arrangement which provides the advantages of pressure injection of the chemical whilst providing fast response between a decision to apply a chemical or change its application rate and the required change at the spray nozzle.
According to the invention, there is provided spray apparatus comprising a spray carrier or liquid reservoir, a loop circuit, a first pump for feeding spray liquid from the liquid reservoir to the loop circuit, a spray chemical reservoir, chemical injection means for injecting spray chemical from the spray chemical reservoir into the loop circuit, a spray nozzle, a valve selectively connecting the spray nozzle to the loop circuit, and a second pump in the loop circuit for continuously circulating spray liquid and spray chemical in the loop circuit.
Preferably at least one one-way valve is provided in the loop circuit to ensure liquid flow in one direction only.
The second pump may be positioned in the loop circuit to receive spray liquid directly from the first pump.
The valve selectively connecting the spray nozzle to the loop circuit may be integral with the spray nozzle assembly or alternatively other valve means may be employed, e.g. a conventional boom control valve. In this case the loop circuit may be divided into first and second loops controlled by a boom control valve in one of the loops which also includes the spray nozzle. A part of the two loops including the pump and the chemical injection means, may be common.
From another aspect the invention is an agricultural or horticultural spray vehicle comprising spray apparatus as described above.